Order By with Union Sql Server 2008 - sql-server-2008

Question

CREATE PROCEDURE [dbo].[spReport]
#FromDate DATETIME = NULL,
#ToDate DATETIME = NULL,
#TenantID int ,
#BusinessUnitId int
AS
BEGIN
Declare #listStr Varchar(max), #listValue Varchar(max)
Select
#listStr = COALESCE(#listStr+',' ,'') + FieldLabel
From
(Select Distinct Top 100
FieldLabel, ControlTypeId
From
PaymentCustomFieldDefinitions PCFD
Inner Join
Product P On P.Id = PCFD.ProductId
Where
P.TenantId = #TenantId
Order By
ControlTypeId Desc) R
Set #listStr = ',' + #listStr
Set #listStr = IsNull(#listStr, '')
Select
'Confirmation Number,Business Unit,Bank Account,Merchant Account,Product Name,Payment Date,Payment Time,Total Amount,Status,First Name,Last Name,Payment Method' + #listStr
Union
SELECT
p.ConfirmationNumber + ',' + bu.Name + ',' + p.TenantBankAccountName + ',' + Case When ma.Name IS NULL then '' ELSE ma.Name END + ',' + pd.Name + ',' +
cast(P.PaymentDate as Varchar(11)) + ',' + convert(VARCHAR(8), P.PaymentDate,108) + ',' + Cast(p.TotalDue As Varchar(20)) + ',' + p.PaymentStatusText + ',' + p.PayorFirstName + ',' + p.PayorLastName + ',' + p.PaymentMethodText + ',' + [dbo].[GetPaymentReferenceAndCustomFields](p.Id,#listStr)
FROM
Payment p
INNER JOIN
Product pd ON p.ProductId = pd.Id
INNER JOIN
BusinessUnit bu ON pd.BusinessUnitId = bu.Id
INNER JOIN
ProductDetailPayment pdp ON p.ProductId = pdp.ProductId
LEFT OUTER JOIN
MerchantAccount ma ON ma.Id = pdp.MerchantAccountId
WHERE
p.PaymentDate BETWEEN #FromDate AND #ToDate
AND p.TenantId = #TenantId AND pd.BusinessUnitId= #BusinessUnitId
ORDER BY
p.ProductId desc
END
Getting this error when using Order by :
Msg 4104, Level 16, State 1, Procedure spReport, Line 41
The multi-part identifier "p.ProductId" could not be bound.
Msg 104, Level 16, State 1, Procedure spQueryPaymentDetailReport, Line 41
ORDER BY items must appear in the select list if the statement contains a UNION, INTERSECT or EXCEPT operator.

Answer 1

You can't reference p.ProductId in the ORDER BY because the first subquery doesn't have a p dataset.
You can't reference a ProductId column in the ORDER BY because there's no column by that name in the combined result set.
To solve these issues, you could add a ProductId column and, if the final output must contain a single column like in your query, use a derived table:
SELECT
p.CSV
FROM (
Select
ProductId = 2147483647,
CSV = 'Confirmation Number,Business Unit,Bank Account,Merchant Account,Product Name,Payment Date,Payment Time,Total Amount,Status,First Name,Last Name,Payment Method' + #listStr
Union
SELECT
p.ProductId,
p.ConfirmationNumber + ',' + bu.Name + ',' + p.TenantBankAccountName + ',' + Case When ma.Name IS NULL then '' ELSE ma.Name END + ',' + pd.Name + ',' +
cast(P.PaymentDate as Varchar(11)) + ',' + convert(VARCHAR(8), P.PaymentDate,108) + ',' + Cast(p.TotalDue As Varchar(20)) + ',' + p.PaymentStatusText + ',' + p.PayorFirstName + ',' + p.PayorLastName + ',' + p.PaymentMethodText + ',' + [dbo].[GetPaymentReferenceAndCustomFields](p.Id,#listStr)
FROM
Payment p
INNER JOIN
Product pd ON p.ProductId = pd.Id
INNER JOIN
BusinessUnit bu ON pd.BusinessUnitId = bu.Id
INNER JOIN
ProductDetailPayment pdp ON p.ProductId = pdp.ProductId
LEFT OUTER JOIN
MerchantAccount ma ON ma.Id = pdp.MerchantAccountId
WHERE
p.PaymentDate BETWEEN #FromDate AND #ToDate
AND p.TenantId = #TenantId AND pd.BusinessUnitId= #BusinessUnitId
) p
ORDER BY
p.ProductId desc
;
The first row is assigned the MaxInt ID value because, as I understand, it is the header row and must go first according to the specified ORDER BY p.ProductId DESC clause (and because I've assumed the ProductId is an int, of course).